TUnit.Mocks: generated generic members drop nullable 'class?' constraint (CS8634) #7305

Description

For a generic method constrained where T : class?, the generated setup/verify extension is constrained where T : class. Setting up the method with a nullable type argument then raises CS8634, which fails builds that treat warnings as errors.

Repro (TUnit.Mocks 1.76.45, net10.0, <Nullable>enable</Nullable>)

public record Foo(string N);
public interface ISvc { Task<T> Get<T>(string key) where T : class?; }

var mock = Mock.Of<ISvc>();
mock.Get<Foo?>(Any()).Returns((Foo?)null);

warning CS8634: The type 'Foo?' cannot be used as type parameter 'T' in the generic type or method
'ISvc_MockMemberExtensions.Get<T>(Mock<ISvc>, Arg<string>)'. Nullability of type argument 'Foo?' doesn't match 'class' constraint.

Expected

The generator copies the constraint's nullability (class?, and likewise notnull / nullable struct forms) onto the generated members.